Technological and environmental problems have persistently arisen as the quest for crude oil and gas becomes more and more acute. Further, it has become necessary to go further offshore in search of adequate production areas. However, the further offshore that one goes, the deeper the water will be.
As a consequence, wellbores are being drilled regularly in greater than one thousand feet of water. While much technology is available regarding the safe and controlled drilling of offshore wells, the problems which arise in conjunction with the deeper waters are becoming increasingly complex.
Further, with the greater depths of water in which it becomes necessary to drill, fixed platforms utilized for producing such wells involves enormous costs. It thus reduces to a question of; is the prospective crude oil-containing reservoir beneath the ocean floor sufficiently abundant to warrant the use of an expensive deep water drilling and/or producing platforms.
Within the past several years, considerable research and development work has been done toward the production of a usable tension leg platform system. In the latter type unit, the basic component comprises a floatable vessel which is capable of adjusting its buoyancy at the water's surface.
A plurality of anchors which have previously been positioned at the ocean floor, are connected to the buoyant vessel by a plurality of holding or pull down cables. It is thus possible, by adjusting the tension on the cables, to position the floating vessel above an area in which a well is to be drilled.
The floating vessel will usually be displaced from directly above a drilling site by surface conditions such as wind and waves, as well as by underwater currents. It is nonetheless possible through the use of supported risers or the like to accomplish drilling operations at great water depths through this type of platform.
A problem which is always present when operating in deep offshore waters, is the possibility that the well or wells being drilled can at any time become uncontrolled or blown out and flow without restraint. This situation has occurred in the past and frequently results in loss of equipment due to damage and/or fire. It also results in the loss of the crude product and the gas both of which flow rapidly to the water's surface.
With the added risk involved in drilling wells in deep waters, it is conceivable that even a minor leak at the ocean floor would permit an uncontrolled and disastrous flow of oil and gas. Such a situation would not only result in the loss of the oil, but could constitute a safety hazard to the immediate environment.
To overcome the above-identified problems and difficulties which are endemic to drilling in deep offshore waters, the present invention is provided. In the later, a drilling vessel having a floatable hull is positioned at the water's surface upwardly, from a well site. Hold down, variable tension cables operably connect to the vessel and extend downwardly to the ocean floor. At the latter the cables are connected to a plurality of prepositioned anchors.
A submergible hull is provided which includes means to removably engage the respective hold down cables. Thus, in the event that an uncontrollably flowing well is encountered, the submergible vessel can be slidably engaged with the hold down cables and controllably lowered to the ocean floor. The submergible hull is provided with a closure member such that upwardly flowing and expanding fluids can be received, and conducted in a controlled manner to the water's surface where they will be collected.
It is therefore an object of the invention to provide an offshore well drilling system which is capable of quickly and effectively confining the effluent from an uncontrollably flowing well. A further object is to provide a tension leg platform system having a detachably positioned submergible portion that can be controllably lowered to the ocean floor by way of the platform's hold down cables.